1. Field of the Invention
The present invention relates to an outflow valve for an aircraft comprising a frame to be disposed in an opening of an outer shell of the aircraft, a first flap pivotably arranged within the frame for controlling a flow cross-section, at least one first inflow opening and at least one outflow opening. The invention also relates to a method for controlling such an outflow valve.
2. Description of Related Art
Outflow valves of the initially mentioned type are used in aircraft to vent the cabin and to adjust the cabin pressure. When air uniformly flows into the cabin, a positive pressure relative to the outside of the aircraft is created within the cabin. The outflow valve of the initially mentioned type allows an adjustable amount of air per unit time to escape through its flow cross-section, which is determined by a flap. This is how the pressure in the interior of the aircraft is adjustable by means of the flap.
After landing it may be found that the cabin pressure in an aircraft has a substantial difference with respect to the pressure on the outside of the aircraft. If the cabin pressure is higher than the pressure on the outside, the doors of the aircraft would be suddenly thrown open by the air pressure upon opening. To avoid this risk the outflow valves of an aircraft are generally fully opened prior to opening of the doors to achieve pressure compensation.
The electronics of an aircraft are cooled by an airflow controlled in a similar manner to the cabin air by means of an inflow valve and an outflow valve. The amount of air necessary for cooling the electronics is often substantially larger than the amount of air necessary to ventilate the cabin.
To protect passengers against undesirable drafts, smells and noises in aircrafts, it is provided to substantially separate the airflows for fresh air supply of the cabin and for cooling of the electronics. The airflows for the main cabin, for example, and the aircraft electronics are thus vented via separate outflow valves.
Only in the case where one or more of the valves fail and remain closed (“failed closed”), the airflows are commonly vented via one of the remaining valves. To enable this, the individual valves must be designed to have a relatively large size. In the case of failure, the airflows may then be redirected in a manner unfavorable for passengers.
An outflow valve of the initially mentioned type is described in US 2004/0217317 A1. The outflow valve described there has a cylinder-shaped valve body and a flap defining a flow cross-section within the cylinder-shaped body and capable of closing off the cross-section. To improve the properties of the valve at small opening angles of the flap, walls have been inserted.
DE 197 13 125 C2 describes a method for regulating the cabin pressure in an aircraft and a stepped valve for use with said method. The stepped valve has a large flap to control an outflowing airflow. A smaller flap is inserted in the large flap for fine control of the airflow.
At large pressure differentials the airflow is controlled by means of the position of the small flap. If the pressure differential is small, the airflow is controlled by means of the position of the large flap.